IP Multimedia Subsystem (IMS) for WCDMA network is defined by 3GPP R5/R6 standard and is an object network by which the 3G mobile networks can realize packet voice and packet data and provide uniform multimedia services and applications. The IMS uses an IP packet domain as its bearer path of control signalings and media transmissions, and adopts session initiation protocol (SIP) as a call control signaling. In the IMS, the user subscription data of the IMS are all managed in a home subscriber server (HSS). Services of the IMS are all provided by an application server (AS), and the session control is accomplished by a serving call session control function (Serving CSCF or S-CSCF), both of which are totally separated in the network architecture. Services are triggered by the S-CSCF to the AS to be processed and a plurality of ASs can co-work with each other. The user accesses the IMS via a proxy node (proxy-CSCF) of his current location, and the session and service control is accomplished by the home domain service node of his registration location. Therefore, the users can always obtain the same services in various access points, and thus the service management, the session control and the bearer access can be separated and the services independent of the position and access can be provided. However, the IMS system architecture defined by the 3GPP does not consider the access of traditional terminal users such as POTS users and ISDN users but only the access of WCDMA and WLAN users.
PSTN and ISDN services generally refer to various types of services provided for plain old telephone network (POTS) users and integrated services digital network (ISDN) users in the traditional public switched telephone network (PSTN) and ISDN networks. Currently, PSTN and ISDN services can be realized by the soft switch network in the packet domain. The soft switch as a call processing node in the soft switch network accomplishes simultaneously the provision of PSTN and ISDN services, and the service control and session control function is realized by the same network node. Since PSTN and ISDN services disperse in various soft switches and are accomplished individually, it is difficult for the call processing nodes to co-work with each other so as to accomplish the services. Moreover, since the user data disperse in various soft switches and the acquirements of user services are restricted to the user's access point, it is difficult to expand uniformly the services.
Currently, non-IMS traditional terminal users are not able to register to and access the IMS domain. Therefore, the problem of how to control the traditional access gateway function (AGF) entity (access device) in the soft switch network to make POTS users and ISDN users access the IMS domain needs to be solved so that the traditional terminal users can similarly receive uniformly value added services and mobility routing services of the IMS network on the premise that the network node functions remain invariable.